Land-based seismic data acquisition and processing techniques are used to generate an image of a geological structure in a subsurface formation. FIG. 1 shows a conventional system for monitoring characteristics of a subsurface formation 105. Conventional systems and methods for monitoring characteristics of a subsurface formation 105 typically include drilling multiple vertical wells 110. Seismic sources 115 are placed into one or more of the vertical wells 110 and seismic receivers 120 are placed into one or more of the vertical wells 110. Wells 110 that contain seismic sources 115 may be referred to as source wells. Wells 110 that contain seismic receivers 120 may be referred to as monitoring wells. Typically, seismic sources 115 and seismic receivers 120 are installed near the surface to reduce installation costs.
Conventional monitoring systems including a network of buried sensors in vertical wells 110 have been used to monitor steam injection in shallow reservoirs, typically between 200 to 1000 meters. Conventional monitoring systems have proven less useful for deeper reservoirs. For example, a deeper reservoir may be located at a depth of around 2,000 meters. Conventional monitoring systems may be hampered by hard formations, which mitigate the seismic response. Likewise, conventional systems that are near surface are less efficient for complex geology. For example, very hard lithographic layers (e.g., anhydrite-type lithography) or inhomogeneous layers diffract seismic energy before it can reach a reservoir being monitored.
Another limitation of conventional monitoring systems is the cost and environmental impact of drilling multiple vertical wells 110. For example, the installation of equipment (such as seismic sources 115 and seismic receiver 120) in tens, hundreds, or more vertical wells 110 can generate permitting issues or, such installation may be forbidden in environmentally fragile areas or in urban areas. What is needed therefore are methods and systems for locating seismic sources and seismic receivers closer to the reservoir and/or decreasing the numbers of holes. What is further needed is a high density of these seismic sources and seismic receivers near the area of interest.